1

SEPTEMBER 2011

Comparing Federal Government Surveys that

Count the Uninsured

Timely and accurate estimates of the number of people who do not have health insurance coverage are

important for understanding trends in health insurance coverage and the impacts of policy changes that affect

health insurance. Estimates of the number of people who are uninsured are available from several different

sources. This brief presents trends in national estimates of uninsurance from four federal surveys, presents

the most recent available state-level estimates from these surveys, and describes the main reasons for

variation in the estimates across the different surveys.

FEDERAL GOVERNMENT SURVEYS USED TO ESTIMATE THE NUMBER OF

PEOPLE WITHOUT HEALTH INSURANCE

This brief compares four federal surveys that are used to estimate the level of uninsurance in the United

States. These include:

The U.S. Census Bureau’s Current Population Survey (CPS): The CPS Annual Social and Economic

Supplement (ASEC) collects data on health insurance coverage. The CPS estimates of health

insurance coverage are among the most commonly cited estimates. The estimates date back to 1987,

and are used to monitor both state and national trends in health insurance coverage.

The National Health Interview Survey (NHIS): Sponsored by the National Center for Health

Statistics, the NHIS includes questions about health insurance coverage, health care utilization and

access, health conditions and behaviors, and general health status, in addition to demographic and

socioeconomic characteristics. The NHIS has been conducted annually since 1957; annual health

insurance coverage estimates are available beginning with 1998.

The Medical Expenditure Panel Survey – Household Component (MEPS-HC): The MEPS-HC is

sponsored by the Agency for Healthcare Research and Quality, and consists of several interviews

with the same respondents over two full calendar years. Conducted since 1996, the MEPS-HC collects

data on health status and health conditions, health insurance coverage, access to and utilization of

health care services, medical expenditures, and various demographic and socioeconomic

characteristics.

The American Community Survey (ACS): Conducted by the U.S. Census Bureau, the ACS is an

annual household survey that replaced the decennial census long form questionnaire. A question on

health insurance coverage was added to the ACS in 2008.

Each of these surveys was designed to collect information for different research and policy purposes. Table 1

summarizes key information from each of these surveys such as who is included in the survey, when and how

the survey is conducted, response rates, and the availability of state-level health insurance estimates.1

2

SEPTEMBER 2011

TABLE 1: Comparison of Federal Surveys Used to Estimate Uninsurance

CPS ACS NHIS MEPS-HC

Sponsor(s) Bureau of Labor Statistics, U.S. Dept. of Labor (conducted by the Census Bureau)

Census Bureau National Center for Health Statistics, Centers for Disease Control and Prevention

Agency for Healthcare Research & Quality (conducted by Census Bureau)

Primary focus Labor force participation and unemployment

General household survey, replaced decennial census long form

Population health Health care access, utilization, and cost

Target population Civilian non-institutionalized population

Entire population Civilian non-institutionalized population

Civilian non-institutionalized population

Sample frame Address-based (Census 2000 sampling frame updated with new construction)

Address-based (National Master Address File)

Address-based (Census 2000 sampling frame updated with new construction)

NHIS respondents

Data collection mode In-person; telephone Mail; in-person; telephone

In-person In-person

Type of uninsurance measures

All of prior calendar year Point in time Point in time; all of prior year; if uninsured, length of time uninsured; uninsured at some point in the past year

Point in time; all of prior year; if uninsured, length of time uninsured; uninsured at some point in the past year

Health insurance coverage: verification question for uninsured

Yes No Yes Yes

State-specific names included for Medicaid/CHIP

Yes No Yes Yes

Response rate 83.8% (2010) 97.5% (2010) 79.5% (2010) 63% (first half of 2009)

Survey period February through April Monthly February, May, August, November

Panel over 2 calendar years

State health insurance estimates

50 states and D.C. 50 states and D.C. 20 largest states Not published

Years available 1987 to 2010 2008 to 2010 1998 to 2010 1996 to 2009

NATIONAL ESTIMATES AND TRENDS

Table 2 shows the most recent available estimates of uninsurance from each of the four surveys. As described

in Table 1, some of the surveys produce estimates of the number of adults who were uninsured for an entire

year, while others estimate uninsurance at a specific point in time (i.e., at the time of the survey), and some

collect multiple measures of uninsurance. The CPS produces the highest estimate of the number of people

without health insurance coverage for the entire year, at 49.9 million people, and the NHIS produces the

lowest, at 35.7 million. The range of the point in time estimates is much smaller (from 47.2 to 48.6 million

people).

3

SEPTEMBER 2011

TABLE 2: Comparison of Uninsurance Estimates (Total Population)

N/A: not available. Sources: CPS estimates from U.S. Census Bureau, 2011, "Income, Poverty, and Health Insurance Coverage in the United States: 2010";

ACS estimates for civilian noninstitutionalized population from U.S. Census Bureau (http://factfinder2.census.gov), accessed September 22, 2011; NHIS

estimates from Cohen et al., 2011, Health Insurance Coverage: Early Release of Estimates from the National Health Interview Survey, 2010”; MEPS

estimates from MEPSNET HC (http://www.meps.ahrq.gov/mepsweb/data_stats/MEPSnetHC.jsp ), accessed September 18, 2011.

Over time, the uninsurance estimates from these surveys have shown similar trends, as shown in Figure 1.

The estimated number of people without health insurance has been rising steadily, driven by an increase in

the number of uninsured nonelderly adults; the number of uninsured children has been trending downward

over the past several years.

STATE-LEVEL ESTIMATES

Both the CPS and ACS are designed to produce state-level estimates for all 50 states and the District of

Columbia. Insurance coverage estimates from NHIS are published for the 20 largest states, and no state-level

estimates of insurance coverage are published from the MEPS-HC.

Table 3 presents the most recent state-level estimates of uninsurance from the CPS, ACS, and NHIS (standard

errors are shown in the Appendix). As with the national estimates, the estimated level of uninsurance for

states varies across surveys; however, general patterns are consistent across the surveys (e.g., states with low

uninsurance rates are low in all three surveys).

FACTORS CONTRIBUTING TO DIFFERENCES IN SURVEY ESTIMATES

There are many reasons why health insurance estimates vary across surveys. The surveys are designed to

fulfill different goals, and use different questions, statistical designs, and data collection and processing

methods. Each of these factors likely contributes to differences in uninsurance estimates.

Specific differences include the following:

Conceptual differences in measures of uninsurance: As noted earlier, some surveys collect

information about whether a person lacked health insurance coverage for a full year, while others

collect information on point in time insurance status, and some collect multiple measures.

Reference period: The CPS Annual Social and Economic Supplement, conducted in February

through April each year, asks respondents about their health insurance coverage during the entire

previous calendar year. Respondents in this survey are being asked to report their coverage for a

time period as long as 16 months prior to the interview. In contrast, NHIS and MEPS have shorter

recall periods, and the ACS collects information only about current coverage. These differences in the

time period for which coverage is being reported contribute to differences in the survey estimates; in

addition, differences in the length of time that respondents are being asked to recall their insurance

coverage status can also result in differences in measurement error across the surveys. 2 In

particular, many researchers believe that the CPS measure is closer to a point in time measure of

uninsurance than a full-year measure.3

Survey Time Period Uninsured for the Entire Year Uninsured at a Specific Point in Time

Number (millions) % of population Number (millions) % of population

CPS 2010 49.9 16.3% N/A N/A

ACS 2010 N/A N/A 47.2 15.5%

NHIS 2010 35.7 11.7% 48.6 16.0%

MEPS 2009 41.5 13.5% N/A N/A

4

SEPTEMBER 2011

FIGURE 1: Trend in Number of Uninsured, 2000 to 2010

20.0

25.0

30.0

35.0

40.0

45.0

50.0

55.0

60.0

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011*

Nu

mb

er U

nin

sure

d (

Mil

lio

ns)

All Ages

CPS

ACS

NHIS

MEPS

20.0

25.0

30.0

35.0

40.0

45.0

50.0

55.0

60.0

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011*

Nu

mb

er U

nin

sure

d (

Mil

lio

ns)

Nonelderly Adults (Ages 18 to 64)

CPS

ACS

NHIS

MEPS

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011*

Nu

mb

er U

nin

sure

d (

Mil

lio

ns)

Children (Ages 0 to 17)

CPS

ACS

NHIS

MEPS

CPS and MEPS estimates are full-year estimates; NHIS and ACS are point in time estimates. *2011 estimates from NHIS are for the first 3 months of the year. Sources: U.S. Census Bureau, "Income, Poverty, and Health Insurance Coverage in the United States: 2010"; Cohen et al. June 2011 and September 2011; Chu and Rhoades 2011 and MEPSNET HC (http://www.meps.ahrq.gov/mepsweb/data_stats/MEPSnetHC.jsp ); ACS estimates for civilian noninstitutionalized population from U.S. Census Bureau (http://factfinder2.census.gov) accessed September 22, 2011.

5

SEPTEMBER 2011

TABLE 3: State-Level Estimates of Uninsurance from Federal Surveys, 2010 (Percent of Population Uninsured)

CPS* ACS NHIS

Full-year Point in time Point in time

United States 16.2 15.5 16.0

Alabama 15.9 14.6 Alaska 17.6 19.9 Arizona 19.0 16.9 26.1

Arkansas 18.9 17.5 California 19.4 18.5 18.6

Colorado 13.8 15.9 Connecticut 11.1 9.1 Delaware 12.1 9.7 District of Columbia 12.4 7.6 Florida 21.3 21.3 21.1

Georgia 19.9 19.7 20.7

Hawaii 7.5 7.9 Idaho 17.2 17.7 Illinois 14.5 13.8 13.0

Indiana 13.6 14.8 13.9

Iowa 11.6 9.3 Kansas 12.8 13.9 Kentucky 15.4 15.3 Louisiana 17.2 17.8 Maine 9.7 10.1 Maryland 13.2 11.3 11.4

Massachusetts 5.0 4.4 4.0

Michigan 13.0 12.4 12.2

Minnesota 8.9 9.1 Mississippi 19.2 18.2 Missouri 14.3 13.2 16.0

Montana 16.6 17.3 Nebraska 12.2 11.5 Nevada 21.0 22.6 New Hampshire 10.1 11.1 New Jersey 15.0 13.2 13.9

New Mexico 21.3 19.6 New York 14.5 11.9 11.1

North Carolina 17.4 16.8 18.1

North Dakota 11.7 9.8 Ohio 13.7 12.3 13.4

Oklahoma 17.5 18.9 Oregon 16.8 17.1 Pennsylvania 11.0 10.2 11.7

Rhode Island 11.7 12.2 South Carolina 18.7 17.5 South Dakota 13.1 12.4 Tennessee 14.9 14.4 17.5

Texas 25.0 23.7 23.1

Utah 13.9 15.3 Vermont 9.5 8.0 Virginia 13.4 13.1 12.9

Washington 13.2 14.2 14.8

West Virginia 13.6 14.6 Wisconsin 9.2 9.4 9.4

Wyoming 16.3 14.9

*CPS state-level estimates are 2-year averages for 2009-2010. Sources: U.S. Census Bureau, "Income, Poverty, and Health Insurance Coverage in the United States: 2010"; Cohen et al. 2011; U.S. Census Bureau, American Fact Finder (ACS estimates for civilian noninstitutionalized population)

6

SEPTEMBER 2011

Differences in survey questions: Differences in the ways that health insurance questions are asked

can lead to differences in uninsurance estimates. For example, when the Census Bureau added a

“verification question” to the CPS in 2000 that asked people who did not report any coverage if they

were in fact uninsured for all of 1999, the estimated number of people without health insurance

declined by 8 percent, from 42.6 million to 39.3 million.4 The CPS, NHIS, and MEPS all verify

insurance status for people who do not report any of the specific types of coverage that the survey

asks about, but the ACS does not. Another difference in survey questions that can lead to different

estimates across surveys is the fact that some of the surveys (CPS, NHIS, and MEPS) use state-specific

names for Medicaid and Children’s Health Insurance Program (CHIP) programs, while the ACS does

not.

Missing data and imputation: All four of the surveys have processes in place to manage missing

data and impute missing values. In the CPS supplement that includes the health insurance questions,

about 10 percent of the respondents do not answer any questions, and the missing values are

imputed by the Census Bureau. Similarly, in the 2008 ACS about 11 percent of responses had one or

more of the health insurance items missing; these missing data were imputed by the Census Bureau.

In contrast, the NHIS and MEPS impute little or no health insurance coverage, because the data are

much more complete than the CPS or ACS.

CONCLUSION

These federal surveys are essential resources for estimating the number of uninsured. Each provides a unique

view of the problem, and together the surveys provide a wealth of information about how uninsurance varies

by population characteristics, and how it is associated with differences in access to and use of health care

services, as well as health status. For state-level analysis, the ACS and CPS are very useful and accessible for

producing comparable estimates across states, and also serve as a valuable source of information for states

that do not conduct their own state-specific insurance surveys.

The exact number of uninsured in the U.S. will never be determined, but available estimates consistently

indicate that the number is large and growing over time. Surveys produce different estimates because they

have different sampling methodologies, survey questions, data collection, and editing procedures.

Understanding these differences is important, but should not distract policymakers from the need to address

issues of cost and access for those without health insurance coverage in the United States.

For additional information comparing survey content and state estimates, see SHADAC’s March 2011 issue brief, “Monitoring the Impacts of Health Reform at the State Level: Using Federal Survey Data.”

7

SEPTEMBER 2011

REFERENCES

2 Klerman JA, JS Ringel, and B Roth. 2005. Under-reporting of Medicaid and welfare in the Current

Population Survey. Working Paper. Santa Monica CA: RAND, March 2005; Short PF. 2001. Counting and

characterizing the uninsured. Working Paper Series. Ann Arbor MI: Economic Research Initiative on the

Uninsured, December 2001; Sudman S, N Bradburn, and S Schwarz. 1996. Thinking about Answers. San

Francisco: Jossey-Bass; Bhandari S. 2004. People with health insurance: A comparison of estimates from

two surveys. Working Paper No. 243. Washington DC: U.S. Census Bureau, June 2004. Available at:

http://www.census.gov/dusd/MAB/wp243.pdf; Lewis, K, MR Elwood, and J Czajka. 1998. Counting the

uninsured: A review of the literature. Washington DC: The Urban Institute, July 1998.

3 Davern M., G. Davidson, J. Ziegenfuss, et al. 2007. “A Comparison of the Health Insurance Coverage

Estimates from Four National Surveys and Six State Surveys: A Discussion of Measurement Issues and

Policy Implications.” Final report for U.S. DHHS Assistant Secretary for Planning and Evaluation, Task 7.2.

Minneapolis, MN: University of Minnesota. Available at: http://www.shadac.org/files/sha-

dac/publications/ASPE_FinalRpt_Dec2007_Task7_2_rev.pdf

4 Nelson, C.T. and R.J. Mills. 2001. “The March CPS Health Insurance Verification Question and Its Effect on

Estimates of the Uninsured.” 2001 Proceedings of the Section on Survey Research Methods, Alexandria, VA:

the American Statistical Association.

8

SEPTEMBER 2011

APPENDIX. Standard Errors for Percent of Population Uninsured, 2010

CPS* ACS NHIS

Full-year Point in time Point in time

United States 0.12 0.06 0.26

Alabama 0.85 0.24 Alaska 0.73 0.67 Arizona 1.15 0.18 1.77

Arkansas 0.91 0.30 California 0.42 0.12 0.65

Colorado 0.67 0.30 Connecticut 0.61 0.18 Delaware 0.79 0.48 District of Columbia 0.91 0.42 Florida 0.61 0.18 0.94

Georgia 0.91 0.24 1.38 Hawaii 0.55 0.30

Idaho 1.21 0.42 Illinois 0.67 0.12 0.86

Indiana 0.79 0.18 1.54 Iowa 1.03 0.18

Kansas 0.91 0.24 Kentucky 1.03 0.24 Louisiana 1.09 0.24 Maine 0.55 0.30 Maryland 0.73 0.18 1.53

Massachusetts 0.36 0.12 0.87 Michigan 0.55 0.12 1.08 Minnesota 0.55 0.18

Mississippi 1.03 0.30 Missouri 0.97 0.18 1.67

Montana 0.91 0.42 Nebraska 0.73 0.24 Nevada 0.97 0.36 New Hampshire 0.55 0.42 New Jersey 0.85 0.12 1.23

New Mexico 1.45 0.42 New York 0.48 0.12 0.74

North Carolina 0.85 0.18 1.17 North Dakota 0.73 0.42

Ohio 0.67 0.12 1.02 Oklahoma 1.27 0.18

Oregon 0.79 0.24 Pennsylvania 0.48 0.12 1.08

Rhode Island 0.73 0.42 South Carolina 0.97 0.24 South Dakota 1.03 0.55 Tennessee 0.79 0.24 1.76

Texas 0.67 0.12 0.91 Utah 0.73 0.36

Vermont 0.67 0.42 Virginia 0.61 0.18 1.24

Washington 0.73 0.24 1.46 West Virginia 0.97 0.36

Wisconsin 0.67 0.12 1.34 Wyoming 0.73 0.67

*CPS state-level estimates are 2-year averages for 2009-2010.

Sources: U.S. Census Bureau, "Income, Poverty, and Health Insurance Coverage in the United States: 2010"; Cohen et al. 2011; U.S. Census Bureau, American Fact Finder (ACS Estimates for civilian noninstitutionalized population)

9

SEPTEMBER 2011

ABOUT SHADAC

The University of Minnesota’s State Health Access Data Assistance Center (SHADAC) is funded by the Robert

Wood Johnson Foundation to collect and analyze data to inform state health policy decisions relating to

health insurance coverage and access to care.

State-level information is needed to plan for implementation of the Affordable Care Act (ACA) and to monitor

its effects over time. Understanding the state-level impacts of the ACA will contribute to better understanding

of the overall impact of the law and help identify any unintended effects.

Our goal is to help states bridge the gap between health data and the policy-making process. SHADAC

produces timely and targeted health policy research with a focus on deriving lessons from state variations in

policy and outcomes in the national context.

SHADAC maintains an ongoing research agenda related to issues of health access and insurance coverage,

data collection methods, and state health policy.

More information is available at www.shadac.org.

State Health Access Data Assistance Center 2221 University Avenue, Suite 345 Minneapolis, MN 55414 Phone (612) 624-4802